1. Field of the Invention
The present invention relates to a control device for controlling an induction type rotating electric machine and a method for controlling the same.
2. Description of Related Art
Conventionally, there has been provided an inverter converting direct current power into alternating current power between a DC power source such as a battery and an AC rotating electric machine. The inverter is provided with a plurality of switching elements such as insulated gate bipolar transistors (IGBT) or metal oxide semiconductor field-effect transistors (MOSFET).
The switching element performs ON/OFF action in response to an instruction signal for driving a rotating electric machine. Here, it has been known that when the frequency of the instruction signal is a low frequency or 0 Hz, inverter lock occurs in which current flows to a particular switching element for a long time. If the amplitude of the instruction signal is large at this time, it comes that a large current flows to a particular switching element for a long time thereby overheating that switching element. Thus, since conventionally, when the inverter lock occurs and then, a large current is detected, inverter protection control for reducing current or voltage to protect the switching element has been performed.
For example, according to Japanese Patent Application Publication No. 2007-259631 (JP 2007-259631 A), if such a control device detects a locked state (state in which the rotation speed is almost zero) of a synchronous type rotating electric machine, it reduces the electric power to be applied to the inverter. According to Japanese Patent Application Publication No. 2012-228131 (JP 2012-228131 A), if the control device detects the locked state of the synchronous type rotating electric machine, it calculates a lockable time which permits the locked state of the synchronous rotating electric machine in response to a coil temperature and an output torque value of the rotating electric machine. According to Japanese Patent Application Publication No. 2005-354785 (JP 2005-354785 A), if the control device detects the locked state of the synchronous type rotating electric machine, it supplies current to the switching elements on which no current is concentrated.
According to Japanese Patent Application Publication No. 8-289405 (JP 8-289405 A), the control device changes the maximum value of the slip frequency for the induction type rotating electric machine in response to the temperature of an electric motor.